Single-wall carbon nanotubes (SWNT) are fullerenes of closed-cage carbon molecules typically arranged in hexagons and pentagons. These carbon cylindrical structures, known commonly as “buckytubes”, have extraordinary properties, including both high electrical and thermal conductivity, as well as high strength and stiffness. For background information on single-wall carbon nanotubes see B. I. Yakobson and R. E. Smalley, American Scientist, Vol. 85, July-August, 1997, pp. 324-337.
Nested single-wall carbon cylinders, known as multi-wall carbon nanotubes (MWNT), possess some properties similar to single-wall carbon nanotubes, however, since single-wall carbon nanotubes have fewer defects than multi-wall carbon nanotubes, the single-wall carbon nanotubes are generally stronger and more conductive.
To exploit the exceptional strength and conductive properties of carbon nanotubes, numerous attempts have been made to incorporate carbon nanotubes into polymers. However, one of the problems encountered in making polymer-nanotube composite blends is the difficulty in achieving a good dispersion of the nanotubes. The better the nanotube dispersion, the more the strength properties of the nanotubes will be conveyed to the polymer composite.
Carbon nanotubes, especially single-wall carbon nanotubes, once in contact, tend to be held tightly together by van der Waals forces. Dispersing single-wall carbon nanotubes is even more difficult than dispersing multi-wall nanotubes because the single-wall carbon nanotubes can “rope” together in aligned bundles of a few to many hundreds of nanotubes. In order to obtain a good nanotube dispersion, van der Waals forces which hold the nanotubes together must be overcome. Means to separate the nanotubes in intimate contact with each other, such as by sonication, can also damage the nanotubes and, consequently, impair strength and tensile properties.
Thus, there is a need for polymer composites comprising carbon nanotubes wherein the nanotubes are well dispersed in the polymer. There is also a need for high strength fibers for applications in articles such as bullet-proof vests, body armor, vehicular armor, ballistic protection equipment, and as reinforcing fibers for both organic and inorganic products, such as in tires, belts, ceramics, polymer laminates for aircraft and other compositions requiring high strength materials. Likewise, there is a need for a method for preparing polymer composites comprising carbon nanotubes wherein the carbon nanotubes are well-dispersed and wherein the structure and properties of the nanotubes have not been adversely affected.